1. Field of the Invention
The present invention relates to a paper stacker for stacking papers with an image recorded thereon in such a state that each set of a predetermined number of papers is displaced or shifted by a given distance on one another which is designed to use with an image forming apparatus such as a copying machine, a printer, a facsimile and a composite machine thereof.
2. Description of the Prior Arts
There is an image forming apparatus, provided with a paper stacker for stacking a predetermined number of papers each with an image recorded thereon as a set in such a manner that each set is displaced or shifted by a given distance on one another. The sets of papers are stored in a state sectioned per set so as to be supplied to a post processing stage such as stapling, folding for book-binding, or the like.
In a conventionally proposed paper stacker, conveyance of supplied papers is stopped by a shift roller, and the papers are shifted together with the shift roller in a direction orthogonal to the paper conveyance direction, that is, in the lateral direction per each paper so as to be stacked.
However, in the above-mentioned paper stacker designed to shift the papers in the lateral direction with respect to their conveyance direction, subsequent papers cannot be fed during movement for shift and therefore the conveyance of papers has to be stopped intermittently in the shifting operation. Moreover, since the shifting operation in the lateral direction should be carried out by a shift roller pair, the shifting mechanism is extremely complicated. In addition, a problem arises in that it can hardly be used for image forming apparatus with a high copying speed, because there is a problem of inertia derived from the mass of the shift rollers.